In the design and construction of fuel hydrant pits it is highly desirable, and in most instances mandatory, that an emergency shutoff valve be disposed between the hydrant riser and the hydrant valve. Conventional fusible link valve assemblies include a valve body, a shutoff disc, a disc seat, a disc shaft, a positive spring actuator assembly, and a bypass valve.
One disadvantage of conventional valves is that their discs are sealably connected to the disc shaft by means of various o-rings disposed about the disc shaft on both sides of the disc mount. The o-rings would melt from the heat of a fire, and hence be destroyed, such that fluid would leak out from the disc shaft and feed the fire. Still another problem resides in the disc mount design itself which in conventional valves causes the shutoff disc to protrude into the fluid flow path while in the open position, thereby restricting fluid flow, creating turbulence and increasing the pressure drop between the hydrant riser and the hydrant valve.
It would be most desirable to design a fusible link shutoff valve which does not leak during normal operations, a valve which is capable of allowing the fluid flow to be bypassed externally when the valve is in the closed position, and a valve which provides unrestricted fluid flow, no turbulence and low pressure drop.
The present invention also provides many additional advantages which shall become apparent as described below.